In gas turbine engines, the air leaving a compressor passes between stationary, or stator vanes, then through a diffuser section. The diffuser has an expanding cross sectional area in the direction of the airflow to decrease the velocity and increase the static pressure of the air. This prepares the air for entry into a combustion section at low velocity to permit proper mixing with fuel.
Gas turbine engines generally require that some compressed air be discharged from a diffuser for operation of aircraft or engine accessories.
A typical prior art diffuser is shown in FIG. 1. The diffuser is sometimes referred to as a diffuser case, because it contains and diffuses the compressed air that exits the compressor. The diffuser comprises an outer wail, an inner wail, which diverge in relation to each other, and a plurality of hollow struts that connect the wails in a first diffuser region. Compressed air from a compressor section passes by the struts. The struts each have a strut bleed, or discharge opening, to allow the compressed air to discharge, or be extracted, into the struts. A portion of the compressed air discharges into the strut opening and flows into a manifold that holds and distributes the discharge air for service applications. The discharge air exits through tubing as needed.
This prior art diffuser discharges the compressed air into the struts prior to reaching a second diffuser region downstream of the struts where the compressed air further diffuses. Discharging the compressed air prior to reaching the second, downstream, diffuser region (as in the prior art) provides an adequate amount of discharge air for some applications, however, it fails to maximize the mount of available discharge air. Applications that require a large volume of discharge air may not be satisfied by the prior design.
In the prior art diffuser, the air that passes the struts enters into the second diffuser region and then into a downstream combustor. The airflow into the second diffuser region and combustor is radially interrupted and distorted because of the struts and the strut discharge process. The interruption of the airflow into the combustor causes interrupted cooling of downstream components, such as the combustor and the turbine. Interrupted cooling of the combustor causes some areas of the combustor to be cooled more than others, this results in uneven radial and circumferential thermal growth and distortion, and eventual combustor and downstream turbine degradation.
Some gas turbine applications may require a large volume of available discharge air. One way to increase the volume of available discharge air is by extracting more compressed air by enlarging the discharge openings in the struts. However, larger strut openings have disadvantages, including, decreasing engine efficiency and increasing airflow interruption through the combustor and turbine regions.
A diffuser is shown in U.S. Pat. No. 3,777,489 that has a plenum located in the diffuser case used to aid in the extraction of compressor air from the diffuser case. The diffuser case disclosed therein, however, does not maximize the amount of available discharge air available for service applications.
A diffuser case that increases the amount of available discharge air and reduces combustor distortion is needed.